Ozone and Carbon Monoxide Observations

Atmos. Chem. Phys., 19, 7233–7254, 2019 https://doi.org/10.5194/acp-19-7233-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. Ozone and carbon monoxide observations over open oceans on R/V Mirai from 67◦ S to 75◦ N during 2012 to 2017: testing global chemical reanalysis in terms of Arctic processes, low ozone levels at low latitudes, and pollution transport Yugo Kanaya1, Kazuyuki Miyazaki2,1, Fumikazu Taketani1, Takuma Miyakawa1, Hisahiro Takashima1,3, Yuichi Komazaki1, Xiaole Pan1,a, Saki Kato3, Kengo Sudo1,4, Takashi Sekiya1, Jun Inoue5, Kazutoshi Sato6, and Kazuhiro Oshima1,b 1Research Institute for Global Change (RIGC), Japan Agency for Marine–Earth Science and Technology (JAMSTEC), Yokohama 2360001, Japan 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA 3Faculty of Science, Fukuoka University, Fukuoka 8140133, Japan 4Graduate School of Environmental Studies, Nagoya University, Nagoya 4648601, Japan 5Arctic Environment Research Center, National Institute of Polar Research, Tachikawa 1908518, Japan 6School of Earth, Energy and Environmental Engineering, Kitami Institute of Technology, Kitami 0908507, Japan anow at: Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China bnow at: Department of Radioecology, Institute of Environmental Sciences, Rokkasho 0393212, Japan Correspondence: Yugo Kanaya ([email protected]) Received: 27 December 2018 – Discussion started: 14 January 2019 Revised: 6 May 2019 – Accepted: 9 May 2019 – Published: 3 June 2019 Abstract. Constraints from ozone (O3) observations over fects of forest fires and fossil fuel combustion were recog- oceans are needed in addition to those from terrestrial re- nized, TCR-2 gave an excellent performance in reproducing gions to fully understand global tropospheric chemistry and the observed temporal variations and photochemical buildup its impact on the climate. Here, we provide a large data set of of O3 when assessed from 1O3=1CO ratios. For clean ma- ozone and carbon monoxide (CO) levels observed (for 11 666 rine conditions with low and stable CO mixing ratios, two and 10 681 h, respectively) over oceans. The data set is de- focused analyses were performed. The first was in the Arc- rived from observations made during 24 research cruise legs tic (> 70◦ N) in September every year from 2013 to 2016; of R/V Mirai during 2012 to 2017, in the Southern, Indian, TCR-2 underpredicted O3 levels by 6.7 ppbv (21 %) on aver- ◦ Pacific, and Arctic oceans, covering the region from 67 S age. The observed vertical profiles from O3 soundings from to 75◦ N. The data are suitable for critical evaluation of the R/V Mirai during September 2014 had less steep vertical over-ocean distribution of ozone derived from global atmo- gradients at low altitudes (> 850 hPa) than those obtained spheric chemistry models. We first give an overview of the by TCR-2. This suggests the possibility of a more efficient statistics in the data set and highlight key features in terms descent of the O3-rich air from above than assumed in the of geographical distribution and air mass type. We then use models. For TCR-2 (CHASER), dry deposition on the Arc- the data set to evaluate ozone mixing ratio fields from the tic ocean surface might also have been overestimated. In the tropospheric chemistry reanalysis version 2 (TCR-2), pro- second analysis, over the western Pacific equatorial region ◦ ◦ ◦ duced by assimilating a suite of satellite observations of (125–165 E, 10 S to 25 N), the observed O3 level more multiple species into a global atmospheric chemistry model, frequently decreased to less than 10 ppbv in comparison to namely CHASER. For long-range transport of polluted air that obtained with TCR-2 and also those obtained in most masses from continents to the oceans, during which the ef- of the Atmospheric Chemistry Climate Model Intercompari- Published by Copernicus Publications on behalf of the European Geosciences Union. 7234 Y. Kanaya et al.: Ozone and carbon monoxide over open oceans: observations and model evaluation son Project (ACCMIP) model runs for the decade from 2000. Alert (82.45◦ N, 62.51◦ W), Barrow (71.32◦ N, 156.61◦ W), These results imply loss processes that are unaccounted for Zeppelin (78.90◦ N, 11.88◦ E), Pallas–Sodankyla (67.97◦ N, in the models. We found that the model’s positive bias pos- 24.12◦ E), Summit (72.58◦ N, 38.46◦ W) and Thule (76.5◦ N, itively correlated with the daytime residence times of air 68.8◦ W) were used to test simulations. Measurements from masses over a particular grid, namely 165–180◦ E and 15– individual cruises (e.g., Dickerson et al., 1999; Kobayashi et 30◦ N; an additional loss rate of 0.25 ppbv h−1 in the grid best al., 2008; Boylan et al., 2015; Prados-Roman et al., 2015), a explained the gap. Halogen chemistry, which is commonly large collection from multiple cruises (e.g., Lelieveld et al., omitted from currently used models, might be active in this 2004), O3 soundings from the SHADOZ network (e.g., Olt- region and could have contributed to additional losses. Our mans et al., 2001; Thompson et al., 2017), and those from open data set covering wide ocean regions is complemen- various campaigns (e.g., Kley et al., 1996; Takashima et al., tary to the Tropospheric Ozone Assessment Report data set, 2008; Rex et al., 2014) have provided important O3 data which basically comprises ground-based observations and over oceanic regions. However, their spatiotemporal cover- enables a fully global study of the behavior of O3. age over open oceans is too sparse to complete the global pic- ture. Aircraft observations (e.g., HIAPER Pole-to-Pole Ob- servations (HIPPO); Wofsy et al., 2011) also sampled marine boundary layer but the measurement frequency was not 1 Introduction necessarily high. One mature example of such global observations that include the over-ocean atmosphere is that for The global burden and distribution of tropospheric ozone CO2. For example, observational data at a large number of (O3) have changed from preindustrial times to the present, remote islands are available from the World Data Centre for and have induced a radiative forcing of C0:4 ± 0:2 W m−2 Greenhouse Gases (WDCGG) database of the World Me- (IPCC, 2013) by interactions with the Earth’s radiative field. teorological Organization (WMO)/GAW. Atmospheric CO2 The distribution of O3 is critical for determining concentra- measurements are now accepted by SOCAT Version 4 (https: tion fields of hydroxyl radicals, which control the lifetimes //www.socat.info/, last access: 27 May 2019), which is a of many important chemical species, including methane. database of ship-based observations, e.g., from research ves- Changes in atmospheric chemistry and their impacts on the sels and voluntary ships. Similarly dense O3 observations climate are often investigated by using O3 distributions de- over oceans are needed. rived from global atmospheric chemistry model simulations. An understanding of the processes behind the O3 mixing Therefore the model performance determines the accuracy ratio distribution is important. Young et al. (2018) reported of the assessment, requiring model evaluation against field that the rates of chemical processes (production and loss) observations of levels of O3 and its precursors. For exam- and deposition/stratosphere–troposphere exchange could dif- ple, the models included in the Atmospheric Chemistry Cli- fer among models by factors of 2–3. More observational con- mate Model Intercomparison Project (ACCMIP; Shindell et straints for characterizing photochemical buildup and long- al., 2011; Lamarque et al., 2013) and the Chemistry–Climate range transport events using tracers such as carbon monox- Model Initiative (CCMI; Morgenstein et al., 2017) were care- ide (CO) are required. The chemical loss term under clean fully evaluated against field observations (e.g., Tilmes et al., marine conditions should also be examined; the loss rate 2016). Recently, an unprecedented comprehensive data set caused by halogen chemistry and the regions where such of O3 measurements was systematically compiled under a chemistry is important need to be evaluated. community-wide activity, i.e., the Tropospheric Ozone As- Since 2010, we have conducted ship-borne observations sessment Report (TOAR) (Cooper et al., 2014; Schultz et al., on R/V Mirai of the atmospheric composition, including the 2017; Gaudel et al., 2018), and this provided additional con- O3 and CO levels, for more than 10 000 h. The geographi- straints for model simulations. cal coverage was wide, covering the Arctic, Pacific, Indian, However, even with the data in the TOAR, observa- and Southern oceans. Such observations, together with cur- tion data coverage over oceans is still poor; Schultz et rently available data sets, will enable critical testing of model al. (2017) reported that the “true oceanic sites” covered simulations that cover the entire globe. In this paper, we ◦ ◦ by TOAR were American Samoa (14.25 S, 170.56 W), present our observational data set for O3 and CO for the Sable Island (43.93◦ N, 59.90◦ W), the Ieodo Ocean Re- first time. The data were separately analyzed for cases af- search Station (32.12◦ N, 125.18◦ E), Ogasawara (27.08◦ N, fected by long-range transport and those under clean marine 142.22◦ E), and Minamitori Island (24.28◦ N, 153.98◦ E), conditions. For each case, the observations were compared while Cape Grim (40.68◦ S, 144.69◦ E), Amsterdam Island with independent reanalysis data from Tropospheric Chem- (37.80◦ S, 77.54◦ E), and Mace Head (53.33◦ N, 9.90◦ W) istry Reanalysis version 2 (TCR-2). The aims are to interpret were also included in other categories. For assessment the observations and to evaluate the reanalysis data over the of the Arctic region (AMAP, 2015), observations ob- oceans.

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